Nitrocellulose base propellants

ABSTRACT

1. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of ABOUT 0.4-10% BY WEIGHT EACH OF A LEAD SALT OF A FATTY ACID AND A MONOALKALI METAL SALT OF A UREIDE ABOUT 40-60% BY WEIGHT OF NITROCELLULOSE CONTAINING ABOUT 1014.2% NITROGEN ABOUT 20-35% BY WEIGHT OF A NITRATE ESTER OF A POLYHYDROXY ALCOHOL, ABOUT 5-25% BY WEIGHT OF AN ACETATE ESTER OF A POLYHYDROXY ALCOHOL, AND ABOUT 0.5-5.0% BY WEIGHT OF A STABILIZER SELECTED FROM THE GROUP CONSISTING OF ETHYL CENTRALITE AND 2NITRODIPHENYLAMINE.

United States Patent 1 1 1111 3,890,175

Lavitt June 17, 1975 NITROCELLULOSE BASE PROPELLANTS Primary Examiner-Stephen J. Lechert, Jr. ir Y'd Si t l i rgirneyxiiel nt, orEFzzlrg rNathan Edelberg; Robert P.

ssignee: e m e a es 0 merlca as 1 son; lctor r 1 a represented by the Secretary of the Army, Washmgton, D.C EXEMPLARY CLAIM Filedi P 1964 1. An improved nitrocellulose base propellant having [21] Appl 394,633 reduced smoke and moisture vapor content in its products of combustion, sa1d propellant cons1st1ng essentially of 5 (5|. 149/92; 149/% 8 about 04-10% by weight each Of a lead Salt of a fatty n I u u 6 l I 6 a 6 I I I v 6 6 u l 6 6 I I I -6 l 58 Field 61 Search 149/19, 92, 96, 102, 97, and a mmalkalf metal a 149/98 99 100 about 40-60% by we1ght of nitrocellulose contalnmg about l0-l4.2% nltrogen [56] References Cited about 20-35% by weight of a nitrate ester of a UNITED STATES PATENTS p y y y alcohol,

2,557,463 6/1951 Pring 194/98 x out 25 by weight of an acetate ester of a 3,033,117 5/1962 Bonner 149/99 X polyhydroxy alcohol, and about 0.5-5.0% by weight of 3,102.834 9/1963 Camp et al. 9/98 X a stabilizer selected from the group consisting of ethyl 2121 ig-l g2 centralite and 2-nitrodiphenylamine.

3:264:993 8/1966 De Fries et al. 149/96 x 8 Claims, No Drawings NITROCELLULOSE BASE PROPELLANTS The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to propellants and more particularly concerns nitrocellulose base propellants having reduced smoke and moisture vapor content in their combustion products.

The presence of smoke by burning propellants can easily reveal the location of artillery or riflemen. Efforts to reduce this telltale smoke have resulted in so called nitrocellulose smokeless propellants (singlebase propellants) and nitrocellulose base propellants which are usually plasticized mixtures of nitrocellulose and higher energy plasticizers such as nitroglycerin (double-base propellants) with or without the addition of other plasticizers, stabilizers or additives. While these prior efforts have been generally successful in that the amount of smoke generated by burning propellants has been reduced, sharpsighted observers and enemy personnel can oftentimes still detect the location of our forces. Additional smoke-reducing efforts have produced propellants yielding higher flame temperatures, but their adverse effect on gun life presents other serious problems.

With the coming of the rocket, the use of propellants has been further extended to gas generants, rocket motors, etc. The introduction thereinto of composite propellants comprising ammonium nitrate in an organic matrix such as cellulose acetate produced relatively smokeless propellants but introduces several objectionable features: (1) hygroscopicity of ammonium nitrate, (2) susceptibility to disintegration of ammonium nitrate resulting from phase changes thereof, (3) inferior ballistics, (4) undesirable high water content in combustion products thereof and (5) difficulty of ignition.

The hygroscopicity of ammonium nitrate gives rise to high manufacturing costs since air-conditioned facilities are required to insure a generally moisture-free environment for the finished grain. It is also known that repeated temperature changes can cause crystalline phase changes in the ammonium nitrate, which result in its eventual disintegration. Further, subjecting these ammonium nitrate grains to adverse temperature conditions markedly adversely affect the burning rate versus pressure characteristics of ammonium nitrate propellants.

Other disadvantages of ammonium nitrate propellants reside in their difficulty of ignition especially in the presence of moisture, and this difficulty is further increased if low temperatures cause the precipitation of frost on the propellant grains. Undesirably high amounts of water in the exhaust of ammonium nitrate propellants may produce a dense contrail in the atmosphere behind a flying missile which restricts observation of the missile and can prevent accurate control thereof.

It is therefor a broad object of this invention to provide improved nitrocellulose base propellants for use in auxiliary power units such as gas generators in missiles and the like and as propellants in rocket motors, artillery and small arms ammunition.

Another object of the invention is to provide improved nitrocellulose base propellants characterized by low smoke and moisture content in their products of combustion.

A further object of the invention is to provide nitrocellulose base propellants which are substantially free of the above mentioned disadvantages inhering in ammonium nitrate propellants.

Other and further objects of the invention will be apparent to those skilled in the art upon study of this disclosure.

Briefly, and in accordance with the aforementioned object, I have formulated improved nitrocellulose base propellants consisting of a fuel such as nitrocellulose, and organic oxidizer, plasticizer, stabilizer, combustion catalyst, ballistics modifier and a combustion catalyst, with or without a coolant, which yield admirable results for the uses mentioned above. Compositions produced in accordance with my invention yield exhaust gases containing only about one-half the water found in the exhaust from ammonium nitrate propellants and produce less smoke on combustion than standard nitrocellulose base propellants of equal flame temperature or standard ammonium nitrate propellants.

More specifically, the improved compositions of my invention, on a weight basis, consist of:

l. About 40 to 60% of nitrocellulose comprising about 10 to 14.2% nitrogen, although I prefer to use about 12.6% for ease of manufacture, grain quality and thermodynamic properties,

2. About 20-34% of a nitrate ester of a polyhydroxy alcohol preferably glycerol trinitrate,

3. About 525% of an acetate ester of a polyhydroxy alcohol preferably glycerol triacetate,

4. About 0.5-10% of a lead salt of a fatty acid in an amount sufficient to promote satisfactory combustion and preferably lead stearate,

5. About 05-10% of the monoalkali salt of a ureide in an amount sufficient to obtain optimum combustion and preferably monosodium barbiturate although sodium barbitol has been found satisfactory,

6. About 0.5 to 5.0% of a stabilizer such as ethyl centralite or 2- nitrodiphenylamine,

7. Nitrogen bearing coolants such as oxamide may be added in amounts up to about 25% to obtain required flame temperature and ballistic properties.

The above composition may be manufactured by any of the processes available such as the solventless water slurry process, solvent process, solvent-solventless process, or the plastisol process, although somewhat better mechanical properties and ballistics are usually obtained when the solventless water slurry process is employed.

EXAMPLE NO. I

A 30 lb. mix of an improved nitrocellulose base propellant, hereinafter designated 101 was manufactured by the solventless water slurry process which involved adding 14.49 lbs. of nitrocellulose containing about 12.6% nitrogen to 144.9 lbs. of water at F in a 55 gallon mix can equipped with an air driven mixer. The suspension was mixed for 10 minutes after which 8.40 lbs. of nitroglycerin was added. The suspension was again mixed for 10 minutes and a mixture containing 0.96 lbs. of lead stearate and 0.30 lbs. of ethyl centralite in 7.23 lbs. of triacetin was added. The suspension was mixed again for 30 minutes after which it was poured into a suitable cotton duck bag. The water was then removed by centrifuging the bag in a suitable wringer to form a paste which was screened through a 141 inch X A; inch mesh screen and dried until the moisture content was 812%. The paste was then blended, 0.30 lbs. of sodium barbiturate being added to the paste and standard ammonium nitrate composite propellants with about the same flame temperatures which did not contain both lead stearate and sodium barbiturate, a considerable improvement in transmission of light was during the blending. The paste was then rolled on dif- 5 observed at all temperatures to as low as 55F. ferential speed rolls at 210F with a roll gap of 0.025

. EXAMPLE NO. 11

inch 0.005 inch at roller speeds of 22.5 and 15 rpm to obtain differential speed sheets. These sheets are A 30 lb. mix of 102 was manufactured by the solventthen rolled on the even speed rolls to form even speed less water slurry process which involved adding 14.49 sheets at 140 i F at a roll speed of 11 rpm and a 10 lbs. of nitrocellulose containing about 12.6% nitrogen roll gap of 0,035 inch i 0.005 inch. to 144.9 lbs. of water at 120F in a 55 gallon mix can Strands, about 7 inches X /8 inch X /8 inch, for burnequipped with an air driven mixer. The suspension was ing rate determinations, were then cut from the even mixed for 10 minutes after which 8.40 lbs. of nitroglycspeed sheets, ignited by a hot wire in a closed bomb in erin was added. The suspension was again mixed 10 conventional strand burning apparatus at specified minutes and a mixture containing 0.96 lbs. of lead steatemperatures and pressures. The time required for the rate and 0.30 lbs. of ethyl centralite in 5.38 lbs. of triacignited strand to burn a specified length is used to caletin (glycerol triacetate) was added. The suspension culate the strand burning rate of the propellant. was again mixed for 10 minutes and 1.50 lbs. of oxam- The remainder of the even speed sheets were cut into ide (5 i 2 microns) was added. The slurry was mixed approximately 2 inches diameter discs and extruded 0 for 30 minutes after which the sodium barbiturate was through a vertical solventless press through a die apadded and the paste processed in the same manner as proximately 2 inches diameter with a 0.5 inch diameter in Example 1 Grains eXmlded, fabricated and pin to obtain grains which were th hi d to h tested as described under Example No. land the results following approximate dimensions: Shown in Table I were Obtained- EXAMPLE NO. 111

Length inches :7225 Three lbs. mixes were manufactured by the sol- OD. inches 1.75 ventless slurry process, using the weights of ingredients O5 wshown below:

, 30 TABLE 11 A nozzle was then selected from calculations based on the strand burning rates above mentioned to propropellant Designation 132 300 332 duce a chamber pressure of approximately 1,000 psi.

When the machined grain was fired in a standard 2 fii f q lbs 13-80 13-30 13-80 inch rocket test motor with the calculated nozzle diam- 5 5,18 3:22 eter and the attenuation of a beam of light by the ex- Sodium Barbitui'ate, lbs .30 0.90 0.90

- Ethyl Centralite, lbs .30 0.30 0.30 haust gases was measured and compared to similar data Lead stearate lbs 96 096 for other propellants at ambient temperature, the fol- Oxamide, lbs 4.50 4.50 4.50 lowing data were Obtained: Water at 120F, lbs 138. 1381 138.

TABLE 1 Designation 101 102 103 104 105 106 107 MDB-7" LF'r-3 Composition, 7o (nominal) Nitrocellulose (12.6%N) 48.3 53.3 48.3 48.3 48.6 48.2 48.1 48.6 Nitroglycerin 27.0 24.2 27.0 27.0 27.0 26.0 27.0 27.0 Triacetin 19.5 14.2 12.5 7.5 19.9 14.5 20.4 18.8 Ethyl Centralite 1.0 0.9 1.0 1.0 3.0 2.8 3.5 1.1 Lead Stearate 312 3.0 3.2 3.2 1 5 1.5 4.6 Sodium Barbiturate 1.0 0.6 3.0 3.0 1.0 1.0 Oxamide 3.8 5.0 10.0 6.0

Calculated Flame Temp, F 2523 2715 2646 2747 2462 2460 2450 2480 1808 Heat of Explosion (Expt), 700 726 715 727 699 698 704 705 734 cal/gm Static Firing Data Pressure. psi 710 960 690 1 138 1340 1130 910 960 650 Burning Time, sec 1.59 1.24 1.74 1.18 1.36 1.31 1.78 1.35 3.48 Mass Rate of Discharge 0.340 0.556 0.396 0.585 0.478 0.519 0.376 0.489 0.198 lb/sec Light Attenuation, 317 2.0 4.7 4.4 21.4 16.3 17.4 7.9 2.5 Specific Attenuation 10.9 3.6 11.8 7.3 44.8 31.4 46.3 16.1 12.6

"Standard type nitrocellulose base propellant Standard type ammonium nitrate composite propellant "Specific attenuation Light attenuation divided by Mass Rate of Discharge When the attenuation ofa beam of light by the eX- These slurries were prepared by the method dehaust products of combustion of compositions desigscribed under Example No. 11 except that lead stearate nated 101, 102, 103 and 104, in test motors was comwas omitted for propellant 300. Grains were extruded,

pared to the attenuation caused by the exhaust products of other standard nitrocellulose base propellants fabricated, and tested as described under example No. l and the results given below:

TABLE 111 Propellant ldentification 132 300 332 Composition,

Nitrocellulose 12.6%N) 46.06 45.89 46.39 Nitroglycerin 25.50 25.06 25.70 Triacetin 8.52 9.83 6.84 Ethyl Centralite 1.06 1.02 1.05 Lead Stearate 3.90 3.48 Sodium Barbiturate 1.04 3.02 3.08 Oxamide 13.92 15.18 13.46

Calculated Flame Temp, F 2424 2424 2413 Heat of Explosion (Expt) 690 696 695 cal/gm Static Firing Data Pressure, psi 1032 959 853 Burning Time, sec 1.50 1.60 1.45 Mass Rate of Discharge, 0.460 0.431 0.476 lb/sec Light Attenuation, 7.0 7.5 4.0 Specific Attenuation 17.4 8.4

From the data shown in Tables I and 111 it is evident that the concurrent use of ideal proportions of lead stearate and sodium barbiturate in propellant compositions of the three classes listed under the examples in this disclosure result in a marked reduction in smoke evolved by the propellant. This reduction in smoke is believed due to some synergistic interaction of the lead stearate and sodium barbiturate in which proper quantities of the two salts produce more complete oxidation of the exhaust products than either salt is capable of producing alone. The proportion of lead stearate and sodium barbiturate must be optimized for each composition. The importance of using two catalysts in optimum quantities is demonstrated by the higher smoke values shown in Table l for Propellants 105, 106 and 107.

It is possible that this same effect may be obtained by the concurrent use of the lead salt of several other fatty acids, for example, lead oleate and the sodium salt of a ureide such as sodium barbiturate or sodium barbitol. It is also possible that similar or even more dramatic results could be obtained by the concurrent use of some other organic lead and sodium salts.

It should also be noted that it is possible that this effect of the concurrent use of a lead salt and sodium salt of the type described above may also be obtained in compositions in which the nitrate ester of the polyhydroxy alcohol is glycol dinitrate or the acetate ester of the polyhydroxy alcohol is glycol diacetate or the acetate ester is replaced by diethylphthalate or dibutyl phthalate.

In addition, nitroguanidine, guanidine nitrate, or urea might be suitable substitutes for oxamide as a coolant.

None of the propellant compositions designated 101 102, 103 and 104, nor any of the ingredients used in their manufacture are hygroscopic. No special precautions or equipment are required to protect the ingredients, composition or finished grains from moisture or humidity. These propellants are readily ignited and the ignition characteristics are not readily affected by high humidity conditions. The ballistic superiority of nitrocellulose base propellants over ammonium nitrate composites are retained and the propellant grains may be cycled through temperature extremes of $165 and --65 repeatedly without any significant deleterious effect on the grain or its ignitability.

1 claim:

1. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 0.5-10% by weight each of a lead salt of a fatty acid and a monoalkali metal salt of a ureide about 40-60% by weight of nitrocellulose containing about l0-l4.2% nitrogen about 20-35% by weight of a nitrate ester of a polyhydroxy alcohol,

about 525% by weight of an acetate ester of a polyhydroxy alcohol, and about 05-50% by weight of a stabilizer selected from the group consisting of ethyl centralite and 2-nitrodiphenylamine.

2. The improved propellant of claim 1 further characterized by the addition of up to about 25% by weight of oxamide.

3. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 05-10% by weight each of lead stearate and monosodium barbiturate,

about 40-60% by weight of nitrocellulose containing about 12.6% nitrogen,

about 2035% by weight of glycerol trinitrate,

about 5-25% by weight of glycerol triacetate about 0.5-5.0% by weight of a stabilizer selected from the group consisting of ethyl centralite and 2-nitrodiphenylamine.

4. The composition of claim 3 wherein up to about 25% oxamide is added as a coolant.

5. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its prod- 5 ucts of combustion, said propellant consisting essentially of about 48.3% by weight of nitrocellulose containing about 12.6% nitrogen,

about 27.0% by weight of nitroglycerin,

about 19.5% by weight of triacetin,

about 1.0% by weight of ethyl centralite,

about 3.2% by weight lead stearate, and

about 1.0% sodium barbiturate.

6. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 53.3% by weight of nitrocellulose containing about 12.6% nitrogen,

about 24.2% nitroglycerin,

about 14.2% triacetin about 0.9% ethyl centralite,

about 3.0% lead stearate,

about 0.6% sodium barbiturate, and

about 3.8% oxamide.

7. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 48.3% by weight of nitrocellulose containing about 12.6% nitrogen,

about 27.0% nitroglycerin,

about 12.5% triacetin,

about 1.0% ethyl centralite,

about 3.2% lead stearate,

about 3.0% sodium barbiturate, and

about 5.0% oxamide.

7 8 8. An improved nitrocellulose base propellant having about 7.5% triacetin, reduced smoke and moisture vapor content in its prodabout 10% ethyl centralite, nets of combustion, said propellant consisting essenabout 32% lead Stearate, tlally of about 48.3% by weight of nitrocellulose containing 5 about 30% Sodlum barbiturate and about 12.6% nitrogen, about 10.0% oxamide.

about 27.0% nitroglycerin, 

1. AN IMPROVED NITREOCELLULOSE BASE PROPELLANT HAVING REDUCED SMOKE AND MOISTURE VAPOR CONTENT IN ITS PRODUCTS OF COMBUSTION, SAID PROPELLANT CONSISTING ESSENTIALL OF ABOUT 0.5-10% BY WEIGHT EACH OF A LEAD SALT OF A FATTY ACID AND A MONOALKALI SALT OF A UREIDE ABOUT 40-60% BY WEIGHT HOF NITROCELLULOSE CONTAINING ABOUT 10-14.2% NITROGEN ABOUT 20-35% BY WEIGHT OF A NITRATE ESTER OF A POLYHYDROXY ALCOHOL, ABOUT 5-25% BY WEIGHT OF AN ACETATE ESTER OF A POLYHYDROXY ALCOHOL, AND ABOUT 0.5-5.% BY WEIGHT OF A STABILIZER SELECTED FROM THE GROUP CONSISTING OF ETHYL CENTRALITE AND 2-NITRODIPHENYLAMINE.
 2. The improved propellant of claim 1 further characterized by the addition of up to about 25% by weight of oxamide.
 3. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 0.5-10% by weight each of lead stearate and monosodium barbiturate, about 40-60% by weight of nitrocellulose containing about 12.6% nitrogen, about 20-35% by weight of glycerol trinitrate, about 5-25% by weight of glycerol triacetate about 0.5-5.0% by weight of a stabilizer selected from the group consisting of ethyl centralite and 2-nitrodiphenylamine.
 4. The composition of claim 3 wherein up to about 25% oxamide is added as a coolant.
 5. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 48.3% by weight of nitrocellulose containing about 12.6% nitrogen, about 27.0% by weight of nitroglycerin, about 19.5% by weight of triacetin, about 1.0% by weight of ethyl centralite, about 3.2% by weight lead stearate, and about 1.0% sodium barbiturate.
 6. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 53.3% by weight of nitrocellulose containing about 12.6% nitrogen, about 24.2% nitroglycerin, about 14.2% triacetin about 0.9% ethyl centralite, about 3.0% lead stearate, about 0.6% sodium barbiturate, and about 3.8% oxamide.
 7. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 48.3% by weight of nitrocellulose containing about 12.6% nitrogen, about 27.0% nitroglycerin, about 12.5% triacetin, about 1.0% ethyl centralite, about 3.2% lead stearate, about 3.0% sodium barbiturate, and about 5.0% oxamide.
 8. An improved nitrocellulose base propellant having reduced smoke and moisture vapor content in its products of combustion, said propellant consisting essentially of about 48.3% by weight of nitrocellulose containing about 12.6% nitrogen, about 27.0% nitroglycerin, about 7.5% triacetin, about 1.0% ethyl centralite, about 3.2% lead stearate, about 3.0% sodium barbiturate, and about 10.0% oxamide. 